1. Field of the Invention
The present invention relates to a method for stripping a lithographic pellicle that is used as a debris shield for a lithographic mask when producing a liquid crystal display panel or a semiconductor device such as an LSI or a ULSI, and a stripping apparatus used therein.
2. Description of the Related Art
In the production of a semiconductor such as an LSI or a VLSI or the production of a liquid crystal display panel, a pattern is formed by irradiating a semiconductor wafer or a liquid crystal substrate with light through an exposure master plate; if debris is attached to the exposure master plate used here, since the debris absorbs the light or bends the light, there are the problems that the replicated pattern is deformed, the edge becomes rough, or the background is stained black, thus impairing the dimensions, quality, appearance, etc. The ‘exposure master plate’ referred to in the present invention is a general term for lithographic masks and reticles.
These operations are usually carried out in a clean room, but even within a clean room it is difficult to always keep the exposure master plate clean, and a method is therefore employed in which a pellicle that allows exposure light to easily pass through is adhered to the surface of the exposure master plate to act as a debris shield.
In this case, the debris does not become attached directly to the surface of the exposure master plate but becomes attached to the pellicle film, and by focusing on a pattern of the exposure master plate when carrying out lithography the debris on the pellicle film does not become involved in the replication.
The pellicle is basically constituted from a pellicle frame and a pellicle film stretched over the frame. The pellicle film is formed from nitrocellulose, cellulose acetate, a fluorine-based polymer, etc., which allows exposure light (g rays, i rays, 248 nm, 193 nm, 157 nm, etc.) to easily pass through. The pellicle frame is formed from a black-anodized etc. A7075, A6061, A5052, etc. aluminum alloy, stainless steel, polyethylene, etc. The pellicle film is adhered by coating the upper part of the pellicle frame with a good solvent for the pellicle film and air-drying or by means of an adhesive such as an acrylic resin, an epoxy resin, or a fluorine resin. Furthermore, since an exposure master plate is mounted on a lower part of the pellicle frame, a pressure-sensitive adhesion layer made of a polybutene resin, a polyvinyl acetate resin, an acrylic resin, a silicon resin, etc. and a reticle pressure-sensitive adhesive protecting liner for the purpose of protecting the pressure-sensitive adhesion layer are provided.
The pellicle is installed so as to surround a pattern region formed on the surface of the exposure master plate. Since the pellicle is provided in order to prevent debris from becoming attached to the exposure master plate, this pattern region and a pellicle outer part are separated so that dust from the pellicle outer part does not become attached to the pattern face.
In recent years, the LSI design rule has shrunk to sub-quarter micron, and accompanying this the wavelength of an exposure light source is being shortened, that is, instead of g rays (436 nm) and i rays (365 nm) from the hitherto predominant mercury lamp, a KrF excimer laser (248 nm), an ArF excimer laser (193 nm), an F2 laser (157 nm), etc. are being used. When the wavelength of exposure light becomes shorter, the energy of the exposure light naturally becomes high. When high energy light such as an excimer laser is used, compared with the light of conventional g rays or i rays, the possibility that gaseous material present in the exposure atmosphere will react so as to form foreign matter on the exposure master plate becomes extremely high. Because of this, countermeasures such as minimizing gaseous material within a clean room, carrying out rigorous washing of a reticle, and removing gas-generating substances from materials forming a pellicle have been taken.
In particular, since the pellicle is used by affixing it directly to an exposure master plate, there is a desire for a low gas generation rate for materials forming the pellicle, that is, a reticle adhesive, a film adhesive, an inner wall coating agent, etc., which are formed from organic materials, and improvements have been made. Among them, as the reticle adhesive there is one that employs a silicone resin in order to give lower outgassing, improved UV resistance, and improved chemical resistance. Since silicone resins have excellent chemical stability, it is possible to fix a pellicle onto a reticle without there being any changes over a long period of time. However, when the pellicle is to be stripped from the reticle for replacement, it is difficult to carry out stripping well without leaving a residue on the reticle. As a method for stripping a pellicle that has a silicone adhesive, a method in which a substrate from which a pellicle is stripped is heated has been proposed (JP-A-2000-305252 (JP-A denotes a Japanese unexamined patent application publication.)).